Among the recognized architectures for data processing systems is the well known bus oriented system in which the various subsystems communicate with one another through a common bus. In bus oriented systems, it is necessary for a source subsystem to ascertain the availability of and obtain the attention of the destination subsystem. In the prior art, this function has typically been carried out using the so-called "broadcast" technique in which the source subsystem places the address of the destination subsystem on address lines constituting a section of the common bus. The destination subsystem must respond with a "handshake" message indicating its status and availability. After analyzing the handshake message, the source subsystem may then proceed to request access to the bus for the purpose of transmitting the message. The broadcast technique, of course, has many variants, but the common thread among them is the necessity for the issuance of a preliminary inquiry from the source to the destination and a definite response from the destination to the source before actual information transfer can commence.
Those skilled in the art will appreciate that an increase in system speed could be obtained if the necessity for the preliminary addressing and acknowledgment dialog between source and destination subsystems could be eliminated.